1. Field of the Invention
The present invention relates generally to hybrid drill bits that are used to drill boreholes in subterranean earth formations. More specifically, the present invention relates to techniques for modeling hybrid drill bits, simulating operation of hybrid drill bits, designing hybrid drill bits, optimizing drilling performance of hybrid drill bits, and displaying hybrid drill bits.
2. Background Art
Drill bits are commonly used in the oil and gas industry to drill boreholes (also referred to as “well bores”) in subterranean earth formations. One example of a conventional drilling system for drilling boreholes in subterranean earth formations is shown in FIG. 1. The drilling system includes a drilling rig 10 that is used to rotate a drill string 12 that extends downward into a borehole 14. Connected to the distal end of the drill string 12 is a drill bit 20.
Two common types of drill bits used for drilling boreholes are known and referred to in the art as “fixed-cutter” drill bits and “roller cone” drill bits. A fixed-cutter drill bit 21, as shown in FIG. 2, typically includes a bit body 22 having (i) an externally threaded connection at one end 24 and (ii) a plurality of blades 26 extending from the other end of the bit body 22. The plurality of blades 26 form the cutting surface of the drill bit 21. A plurality of cutting elements 28 are attached to each of the blades 26 and extend from the blades 26. The plurality of cutting elements 28 are used to cut through subterranean earth formations when the drill bit 21 is rotated during drilling. The plurality of cutting elements 28 may be one or a combination of polycrystalline diamond compacts or other cutting elements formed of materials hard and strong enough to deform and/or cut through subterranean earth formations.
A roller cone drill bit 30, as shown in FIG. 3, typically includes a bit body 32 having (i) an externally threaded connection at one end 34 and (ii) a plurality of roller cones 36 (usually three as shown) attached to the other end of the drill bit 30. The plurality of roller cones 36 are able to rotate with respect to the bit body 32. Attached to the plurality of roller cones 36 are a plurality of cutting elements 38 typically arranged in rows about the surface of each of the plurality of roller cones 36. The plurality of cutting elements 38 may be one or a combination of tungsten carbide inserts, milled steel teeth, or other cutting elements formed of materials hard and strong enough to deform and/or cut through subterranean earth formations. Further, hardfacing (not shown) may be applied to the plurality of cutting elements 38 and/or other portions of the drill bit 30 to reduce wear on the drill bit 30 and/or to increase the useful life of the drill bit 30.
Another type of drill bit that may be used to drill boreholes in subterranean earth formations is known and referred to in the art as a “hybrid” drill bit. Hybrid drill bits include a combination of one or more fixed cutting elements (e.g., 28 in FIG. 2) and one or more roller cones (e.g., 36 in FIG. 3). As shown in FIG. 4, a hybrid drill bit 10 typically includes a bit body 12 having an externally threaded connection at one end 14 and a rock cutting structure at an opposite end. A pair of opposing roller cone legs 16 support roller cones 18 and 19. Adjacent to the roller cones 18 and 19, in an opposing relationship, is a pair of fixed bit legs 26 and 29 extending from and welded to the bit body 12. Fixed bit legs 26 and 29 terminate in fixed bit faces 28 and 31. Hydraulic nozzles or openings are formed in each fixed bit face 28 and 31, each opening communicating with a central hydraulic chamber in the bit body (not shown). Several diamond insert cutter blanks 32 are strategically positioned in faces 28 and 31, the diamond cutting face 34 of the insert blanks being so oriented to most effectively remove the ridges between kerfs cut by the tungsten carbide inserts in the adjacent cones 44 and 45.
The insert blanks 32, for example, are fabricated from a tungsten carbide substrate with a diamond layer 34 sintered to a face of a substrate, the diamond layer being composed of a polycrystalline material.
The roller cone 18, journaled to leg 16 of bit body 12, has a plurality of chisel type tungsten carbide inserts 22 inserted in the cone. The inserts are equidistantly spaced in each row and the outermost row on the cone is the gage row 21. The chisel crown 36 of gage inserts 25 are oriented in this gage row in a radial direction substantially parallel with the journal axis of the cone. Referring to both cones 18 and 19, the “A”, “B”, “C” and “D” rows of inner inserts 22 have their chisel crowns oriented in a circumferential direction substantially normal to the journal axis. With this orientation, the chisel crests or crowns 23 tend to penetrate more deeply into the borehole bottom rather than scrape and gouge as would be the normal function of a chisel insert with its crest oriented in a radial direction, especially in an offset type of rock bit.
One example of a hybrid drill bit is disclosed in U.S. Pat. No. 4,343,371 issued to Baker, III et al., which is assigned to the assignee of the present invention.
Significant resources (e.g., time, money) are needed in the design and manufacture of drill bits for use in drilling boreholes. Having accurate models for predicting and analyzing drilling characteristic of drill bits may greatly reduce costs associated with manufacturing drill bits and designing drilling operations because these models may be used to more accurately predict the performance of drill bits prior to their manufacture and/or use for a particular drilling application.
Modeling and simulation techniques for fixed-cutter bits are disclosed in: Sandia Report No. SAN86-1745 by David A. Glowka, printed in September 1987 and entitled “Development of a Method for Predicting the Performance and Wear of PDC Drill Bits”; U.S. Pat. Nos. 4,815,342, 5,010,789, 5,042,596, and 5,131,478; and U.S. patent application Ser. No. 10/888,358. Modeling and simulation techniques for roller cone drill bits are disclosed in: “The Computer Simulation of the Interaction Between Roller Bit and Rock” by D. Ma et al., printed in 1995 as paper no. 29922 in the Society of Petroleum Engineers; and U.S. Pat. No. 6,516,293, which is assigned to the assignee of the present invention.